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Documentation / devicetree / bindings / arm / psci.txt




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Based on kernel version 4.7.2. Page generated on 2016-08-22 22:40 EST.

1	* Power State Coordination Interface (PSCI)
2	
3	Firmware implementing the PSCI functions described in ARM document number
4	ARM DEN 0022A ("Power State Coordination Interface System Software on ARM
5	processors") can be used by Linux to initiate various CPU-centric power
6	operations.
7	
8	Issue A of the specification describes functions for CPU suspend, hotplug
9	and migration of secure software.
10	
11	Functions are invoked by trapping to the privilege level of the PSCI
12	firmware (specified as part of the binding below) and passing arguments
13	in a manner similar to that specified by AAPCS:
14	
15		 r0		=> 32-bit Function ID / return value
16		{r1 - r3}	=> Parameters
17	
18	Note that the immediate field of the trapping instruction must be set
19	to #0.
20	
21	
22	Main node required properties:
23	
24	 - compatible    : should contain at least one of:
25	
26	     * "arm,psci"     : For implementations complying to PSCI versions prior
27				to 0.2.
28				For these cases function IDs must be provided.
29	
30	     * "arm,psci-0.2" : For implementations complying to PSCI 0.2.
31				Function IDs are not required and should be ignored by
32				an OS with PSCI 0.2 support, but are permitted to be
33				present for compatibility with existing software when
34				"arm,psci" is later in the compatible list.
35	
36	     * "arm,psci-1.0" : For implementations complying to PSCI 1.0.
37				PSCI 1.0 is backward compatible with PSCI 0.2 with
38				minor specification updates, as defined in the PSCI
39				specification[2].
40	
41	 - method        : The method of calling the PSCI firmware. Permitted
42	                   values are:
43	
44	                   "smc" : SMC #0, with the register assignments specified
45			           in this binding.
46	
47	                   "hvc" : HVC #0, with the register assignments specified
48			           in this binding.
49	
50	Main node optional properties:
51	
52	 - cpu_suspend   : Function ID for CPU_SUSPEND operation
53	
54	 - cpu_off       : Function ID for CPU_OFF operation
55	
56	 - cpu_on        : Function ID for CPU_ON operation
57	
58	 - migrate       : Function ID for MIGRATE operation
59	
60	Device tree nodes that require usage of PSCI CPU_SUSPEND function (ie idle
61	state nodes, as per bindings in [1]) must specify the following properties:
62	
63	- arm,psci-suspend-param
64			Usage: Required for state nodes[1] if the corresponding
65	                       idle-states node entry-method property is set
66	                       to "psci".
67			Value type: <u32>
68			Definition: power_state parameter to pass to the PSCI
69				    suspend call.
70	
71	Example:
72	
73	Case 1: PSCI v0.1 only.
74	
75		psci {
76			compatible	= "arm,psci";
77			method		= "smc";
78			cpu_suspend	= <0x95c10000>;
79			cpu_off		= <0x95c10001>;
80			cpu_on		= <0x95c10002>;
81			migrate		= <0x95c10003>;
82		};
83	
84	Case 2: PSCI v0.2 only
85	
86		psci {
87			compatible	= "arm,psci-0.2";
88			method		= "smc";
89		};
90	
91	Case 3: PSCI v0.2 and PSCI v0.1.
92	
93		A DTB may provide IDs for use by kernels without PSCI 0.2 support,
94		enabling firmware and hypervisors to support existing and new kernels.
95		These IDs will be ignored by kernels with PSCI 0.2 support, which will
96		use the standard PSCI 0.2 IDs exclusively.
97	
98		psci {
99			compatible = "arm,psci-0.2", "arm,psci";
100			method = "hvc";
101	
102			cpu_on = < arbitrary value >;
103			cpu_off = < arbitrary value >;
104	
105			...
106		};
107	
108	[1] Kernel documentation - ARM idle states bindings
109	    Documentation/devicetree/bindings/arm/idle-states.txt
110	[2] Power State Coordination Interface (PSCI) specification
111	    http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf
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